1. Field of the Invention
The present invention relates generally to electrical circuits and in particular to switched capacitor circuits for use in DC-DC converters and the like.
2. Related Art
DC-DC converters are frequently used when a DC power source, such as a battery, is used to power an electrical device, such as a cellular telephone, designed to operate at a DC voltage level different than that of the DC power source. One typical DC-DC converter utilizes a switched capacitor array circuit which includes a plurality of capacitors and electronic switching circuitry for switching the capacitors into various configurations. An exemplary DC-DC converter which utilizes such a switched capacitor array is disclosed in U.S. Pat. No. 4,451,743 entitled xe2x80x9cDC-DC Voltage Converterxe2x80x9d.
DC-DC voltage converters having switched capacitor arrays usually have fairly high conversion efficiency and can be implemented in integrated circuit form. However, there is an increasing demand for DC-DC converters capable of even high efficiency operation. The present invention is advantageous in that high efficiency operation is achieved. This and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following Detailed Description of the Invention together with the drawings.
A capacitor array circuit for use in a DC-DC converter and the like is disclosed. The array circuit includes at least two capacitors and typically three capacitors. Switching circuitry, such as transistor switches, is coupled to the capacitors and to the input and output nodes of the array together with a third node, typically the circuit common.
The array circuit further includes control circuitry coupled to the switching circuitry for sequentially switching the array through first, second and third differing states. The capacitor configurations produced in each of the states will be such that a voltage is developed across each of the capacitors that will be fixed relative to voltages present at the input, output and third nodes. Stated in other terms, the voltage across the capacitors is forced to a fixed proportion of the voltage at the input node. Thus, for example, should the input voltage be at voltage Vin, the voltage across the capacitors will be approximately K(Vin) where K is a constant.
One aspect of the subject invention is that the three differing states provides a large number of potential gain configurations using a reduced number of capacitors and transistor switches. The large number of high gain configurations enables higher operating efficiency. The fixed voltages across each of the capacitors permits, for example, the capacitors to be connected in series in one or more of the states, with the high impedance node intermediate the capacitors being at a known and controllable voltage to ensure proper operation.